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20.1 Organizing Life on Earth
The organisim's relationships, such as from which organisms it may have evolved, or to which species it is most closely related, are described in a phylogeny.
Information on shared ancestry is provided by phylogenetic relationships.
Scientists use a tool to show the evolution of organisms.
Scientists consider the evolutionary past to be a hypothesis of the trees.
We can show the relationships among different organisms by constructing a tree of life.
We can read a tree like a map.
A common ancestor is represented at the base of many phylogenetic trees.
Plants and animals are compared with other organisms in a small branch in the diagram.
Some trees show relationships with other trees.
The relationship of the three domains of life--bacteria, Archaea, and Eukarya--is shown in both of these trees.
The branching in a tree shows evolutionary relationships.
Although sister taxa and polytomy share an Ancestor, it does not mean that the groups of organisms split or evolved from each other.
Organisms in two taxa may have split, but neither taxon gave rise to the other.
The root of a tree shows the origin of organisms on the tree.
A branch point is where the two lineages separated.
A taxon that evolved early and is unbranched is called a basal taxon.
Sister taxa are two lineages that stem from the same branch point.
A branch with more than one lineage is a polytomy.
The diagrams can be used to understand evolutionary history.
Through the evolutionary branches between the two points, we can trace the path from the origin of life to any individual species.
By tracing back towards the "trunk" of the tree, one can discover the ancestors of a single species.
The tree can be used to study entire groups of organisms.
The rotation at branch points does not change the information.
The information wouldn't change because the taxon's evolution from the branch point was independent of the other.
Data from fossils, from studying the body part structures, or from studying the molecule that an organisms uses, may be used by researchers.
By combining data from many sources, scientists can build a tree of life.
It is easy to assume that more closely related organisms look the same, but it is not always the case.
It is possible for the two groups to appear different than other groups that are not as closely related.
lizards and frog look similar to lizards and rabbits.
A ladder-like tree of vertebrates was roots by an organisms that lacked a column.
Scientists place organisms with different characters in different groups.
Unless otherwise stated, the branches do not account for length of time, only the evolutionary order.
Unless specified on the diagram, a branch's length doesn't typically mean more time passed or less time passed.
The order in which things took place is shown by the tree.
The tree shows that the oldest trait is the vertebral column, followed by hinged jaws and so forth.
A real tree does not grow in one direction after a new branch develops, but a phylogenetic tree does, and like a real tree, it does not grow in only one direction after a new branch develops.
It doesn't mean that a new branch was formed.
It is possible that groups that are not closely related, but evolve under similar conditions, are more similar to each other than to a close relative.
There are interactive exercises that allow you to explore the evolutionary relationships among species.
Think about the organization of a grocery store.
The produce, dairy, and meats departments are in one large space.
Each department divides into aisles, then each aisle is divided into categories and brands, and finally a single product.
This organization is called from larger to smaller, more specific categories.
The Linnaean system is named after Carl Linnaeus, a Swedish botanist, zoologist, and physician.
When one branch ends as a single species, the groups become more specific.
Scientists divide organisms into three large categories after the common beginning of all life.
The classification system uses a hierarchy to organize living organisms.
The wolf and dingo are included in the common dog, Canis lupus familiaris.
There are eight terms in the full name of an organisms.
For the dog, it is: Eukarya, Animalia, Chordata, Mammalia, and Canis.
The names are capitalized except for the species and the names are italicized.
Canis lupus is the scientific name for the dog.
Dogs are in order.
Canidae is the taxon at the family level, and so on.
The dog is a common name that people typically use for organs.
The "familiaris" is a subgroup of Canis lupus familiaris.
Subspecies are members of the same species that are capable of reproducing viable offspring, but they are separate due to geographic or behavioral isolation.
The levels move toward specificity with other organisms.
Plants and butterflies are included in the widest diversity of organisms that the dog shares.
The organisms are more closely related at each level.
The organisms become more similar at each sublevel.
Dogs and wolves are the same species because they can breed and produce viable offspring, but they are different enough to be classified as different subspecies.
There is a link to learning to explore the classifications of thousands of organisms.
About 10% of the species on the planet can be found on this reference site.
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